Professor Johnson Wants to Determine If Eating Chocolate Prior to Taking

Short Answer

Professor Johnson wants to determine if eating chocolate prior to taking a test has a positive impact on his students' test performance.He asks for volunteers from his classes to test his hypothesis.At the end of the term,the professor concludes that the students who ate the chocolate before the exams did better.Unfortunately for the professor,because he did not use __________ prior to his study,it is not considered a true experiment.